Pipettes

Claim 1

A manual pipette comprising a cylindrical barrel which is internally threaded at both ends, a permanent tip threaded into one end of said barrel, said tip having a bore therethrough which is enlarged to provide an internal ledge proximate to where said tip is connected to said barrel, a crossbar grip threaded into the other end of said barrel, said grip having an axial opening therethrough, said opening having a first smaller diameter proximate to where said grip is connected to said barrel and a larger diameter at its remote end, a piston mounted for reciprocating movement within said barrel and extending from within said permanent tip below the ledge formed therein through said barrel and said grip, a stop member secured to said piston, an annular sealing member abutting the ledge formed in said permanent tip through which said piston reciprocates, bushing means abutting said sealinG member, compression spring means positioned between said bushing means and said stop member for biasing said stop member into engagement with said grip and for biasing said bushing means into engagement with said sealing means so as to maintain an air tight seal around said piston, a knob member secured to the remote end of said piston, and a second stop member secured to said piston proximate to said knob member and positioned to limit the displacement of said piston by engaging said grip when said piston is moved a predetermined distance against the bias of said spring means.